Mechanism of heat transfer to fluidized beds

Abstract In order to determine the nature of the resistance controlling heat transfer between fluidized beds and surfaces in contact with them, heat transfer measurements were made on the same solid constituents with several different fluidizing gases. The heat transfer coefficients obtained with fluidized beds are found to be proportional to the square root of the thermal conductivity of the quiescent beds. This result indicates that the process controlling fluidized heat transfer may be considered to be an unsteady‐state diffusion of heat into mobile elements of quiescent bed material. This picture is analyzed mathematically to yield an equation for the heat transfer coefficient h = h \documentclass{article}\pagestyle{empty}\begin{document}$ h = \sqrt {{\rm K}_{\rm m} \rho _{\rm m} cS} $\end{document} wherein the effects of the bed thermal properties are separated from the effects of the stirring factor S , which accounts for bed motion and geometry. The mass transfer analogue is also derived and shown to correlate existing mass and heat transfer data reasonably well. It is concluded that the proposed mechanism yields a satisfactory picture of the fluidized heat transfer process and may provide the beginnings of a rational approach to the correlation and prediction of fluidized heat transfer in engineering work.